Bones, Bones, and more Bones! Types of Bones Bones, Bones, and more Bones!

Objectives I will be able to: name the four major classifications of bones. identify the major anatomical areas of a long bone. describe the microscopic structure of compact bone.

Bones of the Human Body The skeleton has ~206 bones Two basic types of bone tissue Compact bone tissue Dense Spongy bone tissue Small needle-like pieces of bone Many open spaces

Vocabulary: compact bone: dense bone tissue composed of osteons that makes up the outer layer of flat, short, and irregular bones; major component of long bones spongy bone: internal layer of bone tissue in flat, short, and irregular bones, and in the epiphyses of long bones Spongy bone is full of open sections called pores. The pores are filled with marrow, nerves, and blood vessels that carry cells and nutrients in and out of the bone.  Compact bone tissue makes up 80% and spongy bone tissue makes up 20% of all your bone material.

Classification of Bones Long bones Typically longer than wide Have a shaft with heads at both ends Contain mostly compact bone Examples: Femur, humerus

Classification of Bones Short bones Generally cube-shape Contain mostly spongy bone Examples: carpals, tarsals

Classification of Bones Flat bones Thin and flattened Usually curved Thin layers of compact bone around a layer of spongy bone Examples: Skull, ribs, sternum

Classification of Bones Irregular bones Irregular shape Do not fit into other bone classification categories Example: Vertebrae and hip

 How many bones does the typical human body have? What is the difference between compact bone and spongy bone? Give an example of each major bone type? ~206 compact = dense, spongy = full of pores Answers will vary

Classification of Bones on the Basis of Shape

Gross Anatomy of a Long Bone Diaphysis Shaft Made of compact bone tissue Epiphysis Expanded ends of long bones Covered with dense bone tissue Internal structure is spongy bone

Structures of a Long Bone Periosteum Outside covering of the diaphysis Fibrous connective tissue membrane Arteries Supply bone cells with nutrients

Structures of a Long Bone Articular cartilage Covers surface of epiphyses Composed of Hyaline cartilage Decreases friction at joint surfaces

Structures of a Long Bone Medullary cavity Cavity in shaft Contains yellow marrow in adults Contains red marrow in infants

 What is the difference between the diaphysis and the epiphysis? What do we find in the pores of spongy bone tissue? What is the function of articular cartilage? diaphysis is the shaft and made of compact bone, epiphysis is the ends of long bones, covered with dense bone, internal structure is spongy bone marrow, nerves, and blood vessels decreases friction at joint surfaces

Vocabulary osteocyte: a mature bone cell ossification: the process of bone formation osteoblasts: bone-forming cells osteoclasts: large cells that reabsorb or break down bone matrix

Microscopic Anatomy of Bone

Microscopic Anatomy of Bone At the microscopic level, spongy bone tissue is composed of small needle-like pieces of bone called trabeculae and open space (pores). The pores are filled with marrow, blood vessels, and nerves. In compact bone tissue, mature bone cells (osteocytes) are found in the bone matrix in cavities called lacunae.

Microscopic Anatomy of Bone The lacunae are arranged in concentric circles (like tree rings) called lamellae with a canal through the center (Haversian canal). The Haversian canal carries blood vessels and nerves. Together, the lamellae and Haversian canal form a tube-like structure called an osteon or Haversian System. Osteons (Haversian System) are made up of rings of calcium salts and collagen fibers and form the bone matrix.

Microscopic Anatomy of Bone

Microscopic Anatomy of Bone Haversian canals run lengthwise through bone matrix carrying blood vessels and nerves. Radiating from the center canals to the lacunae are the canaliculi (-us). Tiny canals that form a nutrient transport system for the matrix.

 How are lacunae arranged? What is bone matrix composed of? in concentric circles (like tree rings) called lamellae with a canal through the center rings of calcium salts and collagen fibers

Changes in the Human Skeleton In embryos, the skeleton is primarily hyaline cartilage During development (in the womb, and after birth), much of this cartilage is replaced by bone In adulthood, cartilage remains in: Anterior portion of the nose Parts of ribs Joints Ears

Bone Growth: Intramembranous “Between membranes” Compact Bone Spongy Bone Trabeculae Cross-section of a trabecula

Bone Formation: Intramembranous Membranous bones are incomplete at birth Fontanelles: regions of the skull that remain as membranes “Little fountains” Bone formation complete by age ~2

Bone Growth & Maintenance Bone maintenance is an ongoing process. Our bones are not static but living tissue undergoing constant cellular respiration like other cells in our bodies. Bone matrix undergoes constant rebuilding.

Bone Growth & Maintenance The cells involved in this process include: Osteocytes Mature bone cells (bone maintenance) Osteoblasts Bone-forming cells Osteoclasts Bone-destroying cells Break down bone matrix for remodeling and release of calcium

Bone Growth: Endochondral Steps in Bone Growth – Embryo to Child: 1) Beginning in the first month of pregnancy, a cartilage model is produced by chondrocytes. It is surrounded by a membrane, the perichondrium. Ossification begins at about the 6th week. 2) By the 3rd month, a bone “collar” is produced by osteocytes. The perichondrium of the diaphysis is now termed periosteum.

Bone Growth: Endochondral 3) Chondrocytes hypertrophy (enlarge) and cartilage is calcified. 4) A primary ossification center forms. Blood vessels and osteoblasts invade the calcified cartilage Osteoblasts lay down bone matrix Trabeculae are formed

Bone Growth: Endochondral 5) Around the time of birth, secondary ossification centers form in the epiphyses Bone formation is incomplete at birth The skeleton is not complete until the late teens (females) or early twenties (males)

Bone Growth: Endochondral Epiphyseal plates allow for growth of long bone during childhood. New cartilage is continuously formed Older cartilage becomes ossified Cartilage is broken down Bone replaces cartilage

Long Bone Formation and Growth

Bone Growth: Endochondral Bones are lengthened until growth stops. Bones are remodeled continually in response to two factors: The Ca+ level in the blood and The pull of muscles and gravity on the skeleton (stress).

Bone Growth: Endochondral Bones change shape (how? genetic instructions) Bones grow in width (osteoblasts lay down new bone matrix on the outside of the bone and osteoclasts remove bone from the inner face of the diaphysis). Bone remodeling is done by both osteoblasts and osteoclasts.

 How does your pediatrician know when you are done growing? When do your bones typically stop growing? When the epiphyseal plates close the late teens (females) or early twenties (males)

Websites Crash Course – Skeletal System Part 2 https://www.youtube.com/watch?v=DLxYDoN634c